1. Field of the Invention
The present invention relates to a measuring method of a shape of a cross-sectional circle in a direction orthogonal to an axis of a cylinder, and a shape of a cylinder, and a measuring method used for this. In particular, the present invention relates to the technology of contributing to precision measurement at the time of cutting an outer surface of a cylindrical member, as means of obtaining an accurate cylindrical member. The scopes of the measuring technique acquired by the present invention are various. In particular, the present inventor and et al. applied the present invention to an image forming member of an electrophotographic system of copier, laser beam printer, facsimile, or printer, or the measurement of its base substrate, and verified its effects.
2. Related Background Art
Heretofore, a cylindrical member whose shape is finished with predetermined accuracy has been used for an electrophotographic photosensitive drum or a development sleeve in an image forming apparatus such as an electrophotographic system of copier, laser beam printer, facsimile, or printing machine. An electrophotographic photosensitive drum is produced by giving a photosensitive film to a surface of a drum substrate which is finished with predetermined accuracy. Nevertheless, there is a problem that convexo-concave arises in a photosensitive film when the accuracy of dimensions of the drum substrate is low, and for this reason, a defect arises in an image of an image forming apparatus. Hence, in order to obtain high-precision image forming apparatus, high accuracy is required in a cylindricity, a roundness, and the like of the drum substrate.
Furthermore, also in the process of producing such a drum substrate, a highly precise measurement function aiming at assuring the accuracy of dimensions is required, and the following conventional technology is known as methods aiming at it. A method of measuring a surface shape by a zonal laser or other measuring means while standing and rotating a measured cylinder (a cylinder which is a measuring object, and this is the same hereafter) on a rotatable base (for example, refer to Japanese Patent Application Laid-Open No. H06-201375). A method of holding both ends of a measured cylinder with a certain holder and rotating the cylinder, and measuring the size of interrupting a zonal laser to measure cylindrical shape (for example, refer to Japanese Patent Application Laid-Open No. H08-005341). A method of performing measurement by the approximate calculation of the measured values acquired from displacement detectors facing an outer peripheral section of a measured cylinder by rotating the measured cylinder without fixing a rotation axis (for example, refer to Japanese Patent Application Laid-Open No. H06-147879) and the like. Nevertheless, in addition to such a request to extended-definition of an image forming apparatus, a simpler measuring system aiming at the reduction of manufacturing cost becomes indispensable in recent years. Furthermore, with mentioning a cylindrical measuring method with following needs as industrial product evaluation, items to be evaluated should be classified into the accuracy of dimensions as a cylinder, and partial geometrical defects of a surface, and measuring means suitable for each object should be used. Here, according to the measurement of accuracy of dimensions, in a field of measuring the accuracy of dimensions of a circumferential shape of a cylinder, especially a circumferential shape of a cylinder which premises that it has such a high level of accuracy that the present invention may make it an object, it is possible to make it sufficient evaluation even if the number of measured points is a small number comparatively when each measured value is very exact. Hence, industrially, it is preferable to reduce the number of measurement points as much as possible, and to aim at reducing processing time. On the other hand, even if the number of measurement points is increased at the time of evaluating a partial geometrical defect of a cylindrical surface, it is difficult to evaluate all microdefects such as a hairline-like scratch defect. Hence, it is not preferable also in this point to make the number of measurement points increase. Hence, evaluation means by surface defect analysis such as image processing which replaces it should be used. That is, when performing the dimensional accuracy measurement of a circumferential shape of a cylinder as industrial product evaluation, from a viewpoint of pursuing measurement efficiency, it can be said that it is most preferable that there are few loads concerning measurement, each measured value is exact, and the number of measurement points is suppressed to the minimum. In this point, although the conventional method of measuring a surface shape by measuring means such as a zonal laser while standing a measured cylinder on a rotatable base and rotating this (for example, refer to Japanese Patent Application Laid-Open No. H06-201375) can acquire very highly precise measured value, it is not easy to reduce measuring time and loads since preparatory work such as precise centering of the measured cylinder on the base in measurement is required. In addition, the method of holding both ends of a measured cylinder with a certain holder and rotating the cylinder, and measuring the size of interrupting a zonal laser to measure cylindrical shape (for example, refer to Japanese Patent Application Laid-Open No. H08-005341) can perform comparatively simple measurement. On the other hand, the variation of a cylindrical wall thickness affects a measured value, the fitting gap size of the holder of both ends, deformation of ends by a holding force, the vibration of a shaft arising at the time of rotating the measured cylinder, or the like becomes easily a cause of generating a measurement error. Furthermore, the method of performing measurement by the approximate calculation of the measured values acquired from displacement detectors facing an outer peripheral section of a measured cylinder by rotating the measured cylinder without fixing a rotation axis (for example, refer to Japanese Patent Application Laid-Open No. H06-147879) is simple and can suppress an influence of accuracy of an instrument concerning measurement over measurement result. On the other hand, this has a feature that, since the measurement result is approximately calculated values, it increases the accuracy of each measured value to make the number of measurement points and an order of an approximate calculation increase. It is required that the number of measurement points is at least 64 points or 100 points or more. Hence, it is hardly possible by this method to reduce the number of measurement points, and this method takes comparatively long measuring time.
Thus, the conventional technology has not provided a dimensional accuracy measuring method of a circumferential shape of a cylinder as industrial product evaluation which makes loads, concerning measurement, minimum from a viewpoint of measurement efficiency, and makes it possible for each measured value to be exact and to suppress the number of measurement points to the minimum.